Would you mind siting a reputable source for your assertion that "most people are deficient"?
While it is commonly understood that 57% of the population doesn't consume the RDA for magnesium, yet actual magnesium deficiency is uncommon. And I quote:
"Low magnesium is typically due to decreased absorption of magnesium in the gut or increased excretion of magnesium in the urine. Low magnesium levels in otherwise healthy people are uncommon."
And elsewhere in the same article: "An estimated 2 percent of the general population has hypomagnesemia."